This invention relates generally to semiconductor devices, and more particularly to an improved phototransistor and process for fabricating same.
Various types of semiconductor photodiodes have been fabricated which produce current substantially in proportion to the quantum of light striking the diode junction. This type of structure is typically used for infrared detection, but such use generally requires the current to be greatly amplified. Considerable effort has been directed toward developing an integrated circuit capable of both detecting and amplifying the resulting current signal. Phototransistor structures proposed for this purpose are commonly formed by a pair of diffused junctions or by a diffused junction and an alloyed junction. While these devices generally increase the current levels produced for a given photon level, and the detectivity is not particularly high because of the high noise levels associated with the devices.